My prior U.S. Pat. No. 4,011,893 discloses an emitter, or drip irrigation valve, in which the pressure drop across the emitter is obtained by a restricted fluid passage defined by a groove in one surface of the emitter and a resilient element which is contiguous that surface of the emitter. Water flows from an inlet through an aperture in the resilient element and through the restricted fluid passage to an outlet. The pressure drop in the restricted fluid passage is sufficient to provide for the discharge of water at the outlet at a slow trickle or drip rate.
My prior U.S. Pat. No. 3,998,427 discloses a similar drip irrigation emitter, except that the resilient element is in the form of a grid. The grid cooperates with a surface of the emitter to define the restricted fluid passage.
Although these emitters are very satisfactory, it has been found that, on occasion, water leaks out of the restricted fluid passage and gets between the resilient element and the emitter surface to such an extent that the restricted fluid passage is enlarged. This increases substantially the discharge rate of the emitter.